1. Field of the Invention
The present invention relates to mechanical seals, and more particularly to a mechanical seal having angular opposing stationary and rotatable sealing surfaces.
2. Description of the Related Art
Moving parts such as rotating shafts extend from equipment such as pumps. Various means, such as packing can be interposed between stationary elements of the equipment and the rotating element. Particularly useful seals are mechanical seals. A mechanical seal provides a seal between the rotatable element, typically a shaft, and a stationary housing of an apparatus, typically containing fluid. Such seals are often associated with a fluid pump having a shaft extending through a pump housing wall. The pump shaft can be coupled to a motor through a motor shaft. The mechanical seal forms a seal between the pump shaft and the outer surface of the pump housing. Mechanical seals for such applications are commercially available and are described in U.S. Pat. Nos. 4,639,000; 4,832,351; 4,989,882; and 4,993,720. Such seals endure rigorous environments and last for extended time periods.
Seals which are known in the art comprise rotatable components and stationary components which contact to form a seal at opposing sealing surfaces. The rotatable components include a shaft attachment means, Such a means is typically a sleeve or ring having an inner perimeter surface which sealingly fits around the outer perimeter surface of the shaft and is connected to the shaft by connecting means such as set screws. A seal means such as an "O" ring typically provides a seal between the shaft and the sleeve. There is a rotatable circumferential seal element interconnected to the sleeve so as to rotate when the shaft and sleeve rotate. The sleeve extends axially along the shaft.
The stationary components comprise a gland which extends circumferentially around the shaft. The gland abuts against the outer housing surface around the shaft. There is a sealing means, typically a sealing gasket, interconnected to the gland and located between the gland and the housing. The gland functions as a base by which a seal element is attached to the housing. The connection is typically accomplished by bolts extending from the outer housing wall. The bolts are connected to the gland by suitable means such as passing through slots or connecting extenstions extending radially from the gland. The bolts extend through the connecting slots or connecting extensions and are secured with nuts.
A stationary seal element is located between the inner circumferential surface of the gland facing the shaft (i.e. the gland inner surface) and the shaft. The stationary seal element can be directly or indirectly connected to the stationary gland. There are suitable means such as described in U.S. Pat. Nos. 4,832,351 and 4,989,882 to axially center the various stationary elements on the shaft. A circumferential spacing is maintained between the stationary elements, and the shaft and various of the rotating elements.
The stationary and rotatable components meet at opposing sealing surfaces of the rotatable and stationary seal elements. One element is a hard element made of a material such as silicon carbide and the other sealing element is a soft element made of a material such as carbon. There is typically a spring means which forces either one of the seal elements toward the opposing seal element to cause the opposing surfaces to be pressed together. One opposing seal element has restricted axial movement and the surface of the opposing seal element is forced by the spring against the surface of the restricted seal element. Thereby, a seal is formed between the opposing sealing surfaces, i.e., the rotatable and stationary sealing elements.
Opposing rotatable and stationary sealing surfaces known in the art are perpendicular to an axis through the shaft. A problem with such seals is that the shaft typically has some axial play and therefore does not rotate precisely around the shaft axis. The path of one seal surface relative to the other is defined as a track for the purpose the present invention. If the shaft rotates perfectly the sealing surfaces would track perfectly around the circumference of the seal surfaces. As the softer seal element wears, a track pattern forms. Because the shaft rotation is not axially perfect, the rotating seal face wipes across the stationary seal face. The track that forms becomes radially wider than the width of one of the seal elements and a leak forms.
Although known seals are effective to provide a mechanical seals, improvements to prevent fluid leaking at the surface are a continuing goal. This is particularly the case which the seal is used under severe conditions. Such conditions are present when using the mechanical seal with large and heavy pieces of equipment and under conditions where fluid pressure may be continually or intermittently high.
Mechanical seals can comprise one or more one piece circumferential elements which fit over the shaft upon assembly. A specific type of mechanical seal known as a split seal comprises rigid elements which each have two circumferential sections which are connected around the shaft. The sections are circumferentially "split". Various of the rigid sections, including the mechanical seal elements, adaptors, glands, etc. are split. Various elastic seals used can open at one or two points. The advantage of the split mechanical seal is that it can be installed, and maintained without having to disassemble the equipment associated with the shaft to slip a seal apparatus over the end the shaft. The split seal is particularly useful in the maintenance on heavy equipment having shafts of from one to twelve inches or more.
U.S. Pat. No. 5,114,163 discloses a split mechanical face seal having a sealing element that seals a primary ring against a shaft and rigidly positions the primary ring in the axial, circumferential and radial directions. The split seal also includes a sealing element which seals a mating ring against the housing and non-rigidly positions the mating ring in the axial directon while simultaneously providing an axial biasing force on the mating ring to provide mating contact of the two rings.
U.S. Pat. No. 4,576,384 discloses a split mechanical face seal comprising a pair of seal rings. Each ring comprises segments secured about the circumference by securing means. The rings are non-rigidly supported in an axial direction by resilient support means. At least one of the support means comprises biasing means axially biasing the sealing surface of the rings together.
Additionally, various means are known to connect the mechanical seal to the housing. Typically, such means are integrated into the structure of the stationary component. For example, the gland can have extensions which have holes or slots to receive bolts extending from the stationary housing. Nuts can be used to secure the gland, and thereby secure the seal in place. Above referenced and incorporated U.S. Ser. No. 08/057,332 disclosed removeable clips which can be interposed between the housing bolts and the gland to secure the seal in place. Other disclosures of circumferentially adjustable and/or removeable clip means are disclosed in U.S. Pat. Nos. 4,625,977; 5,071,139; and 5,209,496.